Add executable to Options interface to get the name of the executable used to execute the script.

tests/standalone/io/process_stdout_test.dart

Index: tests/standalone/io/process_stdout_test.dart
diff --git a/tests/standalone/io/process_stdout_test.dart b/tests/standalone/io/process_stdout_test.dart
index 7fac576b4f3f5a0052d3efd9351bcde7f7b5c30a..cb6b0a1e19d37e0d286157f6b86f9db9045b76cb 100644
--- a/tests/standalone/io/process_stdout_test.dart
+++ b/tests/standalone/io/process_stdout_test.dart
@@ -67,5 +67,5 @@ main() {
     scriptFile = new File("../tests/standalone/io/process_std_io_script.dart");
   }
   Expect.isTrue(scriptFile.existsSync());
-  test(new Process.start(getDartFileName(), [scriptFile.name, "0"]), 0);
+  test(new Process.start(new Options().executable, [scriptFile.name, "0"]), 0);
 }